Effect of Diameter

ESEM has been successfully used to observe the formation of water plugs inside CNTs from condensation of the vapor present in the microscope chamber. It was found that for a flxed temperature, as the water vapor pressure was increased, water flrst formed a thin fllm on the walls of the CNT, which subsequently thickened to form a plug (Fig. 10.11). 

Interestingly, the onset of water condensation inside the CNTs occurred at a lower than expected vapor pressure (5.6 Torr instead 

(b-e] ESEM images showing how, upon an increase in water vapor pressure, the water begins to form the plug seen in [aj. [with permissions from ref 

A recent investigation of the Tilling of CNTs with nonpolar liquids found that reducing the diameter of the CNT reduces the solid liquid interfacial tension. From theoretical considerations, the authors calculated the surface tension of the CNT to be 50 mN m , close to experimental values found in literature (28-45 mN m ). A transition between Poiseuille laminar flow and ballistic flow inside a CNT below a nm diameter threshold was also obtained from theoretical calculations. 

With their particular structure, CNTs have been the ideal test bed to directly investigate liquid behavior under confinement. Some of these findings are now being tested for applications, in particular in the area of water filtration and desalination.  

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Effect of diameter, size, and orientation of heater Using data available then, Bernath (1960) studied the diameter effect of a horizontal cylindrical heater on the critical heat flux in pools of saturated water at atmospheric pressure. The results indicated that CHF increases as the heater diameter increases up to about 0.1 in. (2.5 mm), then levels off. 

Breen, B. P, and J. W. Westwater, 1962, Effect of Diameter of Horizontal Tubes on Film Boiling Heat Transfer, Chem. Eng. Prog. 58 67. (2)... 

For the forced convective region, only limited data are available on the effects of the different variables involved, since the existence of this region has only been recognized recently. As previously mentioned, the velocity required for the suppression of nucleate boiling increases with pressure further, an increase in pressure reduced the specific volume of the vapour and hence the linear velocity of the two phase mixture at a given quality will be reduced. Thus higher velocities and steam qualities would be required for the forced convective region to be entered at the same heat flux. The effect of diameter is, as far as can be seen from the work of previous experiments and from these experiments, that to be expected with convective heat transfer, namely, that the coefficient is proportional to the diameter or the equivalent diameter to the power —02. 

The effect of diameter has been tested for horizontal hot wires. Rinaldo (M3) used diameters of 0.024 in. and less. The data are shown in Fig. 32. The values at the lowest temperature differences are due probably to free convection rather than to boiling. For the range of... 

Effect of Diameter of the Explosive Composition on the Velocity of Detonation... 

A distinctive feature of fluidized beds is a high rate of heat transfer between the fluid and immersed surfaces. Some numerical values are shown on Figure 17.37. For comparison, air in turbulent flow in pipelines has a coefficient of about 25 Btu/(hr)(sqft)(°F). (a) is of calculations from several correlations of data for the conditions identified in Table 17.19 (b) shows the effect of diameters of quartz particles and (c) pertains to 0.38 mm particles of several substances. 

The data in Refs 32 41 lead to the following tabulation of the effect of diameter of confined 1.47g/cc Tetryl charges on threshold pressure (in the ex pi at its interface with the barrier) ... 

It is expected that the strong dependence on reactor diameter only extends up to a maximum diameter beyond which there is no effect of diameter however, there is disagreement among experts as to what that maximum diameter may be. There are a large number of correlations for liquid axial dispersion with widely different predictions, and care must be exerted to validate the predictions with data at some significant scale, even if only in a cold flow mockup. 

Redistribution of vapor depends on a balance between the vertical and horizontal pressure gradients (157). The horizontal pressure gradient depends on column diameter, and diminishes rapidly as column diameter increases. This explains the strong effect of diameter in item 4 above. Another important factor cited by Porter and Ali (157) is vortex formation. This can cause downward flows of vapor in the bed. Downward flows were actually measured by Kabakov and Rozen (154) and Porter and Ali (157). 

Closely examine the considerations in Sec. 9.3.3. Use these to scale up the HETP from the above steps to your column. Pay attention to effects of diameter, height, and wetting. Judgment is required. It may pay to look at the original reference from which the data were derived in order to check whether distribution, data scatter, or test procedure have influenced the data. 

Fig. 13. Effect of diameter of B2O3 coated vessel on second limits (after Egerton and Warren [24]). o, 7.4 cm diameter X, 3.5 cm diameter , 2.3 cm diameter. (By courtesy of The Royal Society.)...

Table 21.3 Effect of Diameter on Detonation Velocity of Cylindrical Charges Fired in Air...

In this chapter we investigated some of the real effects in explosives. These included, in the nonideal region of detonation, the effects of diameter in lowering the detonation velocity and eventually causing failure in detonation. In ideal detonation we examined the effects of temperature, density, and geometry. 

Fig. 16. Film boiling of oxygen. The effect of diameter of horizontal tubes and wires is demonstrated at one atmosphere. The type of metal has no effect. Data are shown for one line only (Bl).

The data for film boiling permit a discussion of the effect of diameter for horizontal tubes. Equation (1) predicts that h is proportional to D y ... 

Fig. 20. Effect of diameter for film boiling of n-pentane on a horizontal tube at atmospheric pressure. The type of solid has no effect (B3).

Equation (7.70) does not allow for the possible effect of column length, and the effect of diameter may level off for sizes greater than 4 feet. For Z), = 4 ft and Uq = 100 ft/hr, Eq = 5900 ft /hr. With this value for Eq, the Peclet number for a reactor with L = 20 ft and a liquid velocity of 40 ft/hr would be Pe = = 0.14. For Peclet numbers much less than 1.0, the conversion for a first-order reaction is almost the same as for a perfectly mixed reactor, so the assumption of perfect mixing is usually justified for large bubble-column reactors. 

K. M. Becker, Burnout Measurements in Vertical Round Tubes, Effect of Diameter, AE-TPM-RL-1260, 1970, Aktiebolaget Atomenergi, Stockholm. 

Commercialization of new CFB processes for the production of chemicals— specialty or commodity—has been hindered due to scale-up concerns and operational complexity. In particular, the effect of diameter, high solids mass flux, and high pressure on gas hydrodynamics are undocumented in the open literature. Innovative research aimed at the design of new solids feeding devices and gas-solids separation techniques may reduce operational complexities. However, studies on small scale equipment must be performed prudently and documented concisely to be useful for scale-up. Scale effects at the entrance region are considerable, and sufficient attention has not been devoted to this region. 

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